1. 2.1 Plant Cells, Tissues, and Organs

2. Cell Specialization
cell specialization = when young cells develop from similar cells into ones that have specific functions
Occurs in multicellular organisms
Cell differentiation is the development stage in a young organism when specialized cells form
Genes produce the proteins that cause cells to become specialized into a bone cell, nerve cell, muscle cell, ...
all cells contain the same DNA
certain genes “turn on” in one cell type, but not in others
New cells come from pre-existing cells by mitosis (& cytokinesis), but they are not necessarily going to perform the same function

3. In all multicellular plants & animals:
groups of specialized cells form tissues
groups of tissues form organs
groups of organs form systems
In plants, unspecialized cells are called meristematic cells
In animals, unspecialized cells are called stem cells
Meristematic cells are sometimes called ‘permanent embryos’, because unlike many animal stem cells, they can produce cells that will become new tissues & organs at any point in a plant’s life
in humans, true undifferentiated stem cells exist only as a fetus
Plant: meristematic cells  tissues  organs  systems
Animal: stem cells  tissues  organs  systems

4. Plant
Animal

5. Meristematic Cells form Tissues
Meristematic cells are constantly producing new cells
these new cells become specialized to form tissues
Types of plant tissues:
1. Dermal tissue
2. Ground tissue
3. Vascular tissue
Figure 2.3 on p.58

6. Types of Plant Tissues 1. Dermal tissue  outermost part
Made of epidermal cells
These cells act as a barrier by:
protecting the more delicate inner tissues
controlling the exchange of materials
2. Ground tissue  middle layer
Made of photosynthesizing cells & support cells
3. Vascular tissue  innermost tissue
Made of phloem cells & xylem cells
phloem cells transport nutrients like water & sugar throughout the plant
xylem cells provide physical support

8. Replacing Specialized Cells
Cells, tissues, and organs of multicellular animals like humans form as embryos inside the womb
while some of the cells can be replaced, organs have to last for life!
mammals cannot regenerate organs
Unlike many animals, plants can replace cells, tissues and organs throughout their lives
they can produce new cells which will become organs like leaves, roots, & stems
Bud = cluster of meristematic cells that often specialize to form leaf or flower organs
Most of a plant’s growth takes place at the terminal bud
see Figure 2.4 and 2.5 on p. 59
terminal bud produces the plant hormone auxin which ‘holds back’ growth in other places

10. Plant Organs
Tissues working together to form a leaf, one plant organ

11. How many plant organs can you identify in the diagram to the right?
Leaf
Stem
Roots
(Flower)
reproductive organ

12. The Leaf
Its most important job is to provide a large surface area for photosynthesis to take place
Upper surface
Made of a layer of dermal tissue called the epidermis
Epidermal cells secrete a waxy cuticle (top layer) that:
helps reduce water evaporation off of leaf
protects the leaf so it can perform its primary function, photosynthesis
sunlight passes through epidermal cells to photosynthesizing cells

13. Middle surface
Made of mesophyll tissue (a special type of ground tissue), which is composed of 2 types of cells:
palisade cells, which are specialized to perform most of the photosynthesis in the leaf
spongy parenchyma cells, which form a loose network of open spaces (like a sponge), where gases for photosynthesis can be contained (CO2, H2O, O2)
xylem and phloem cells are arranged in bundles that form veins to help the palisade cells conduct photo. & cell resp.
xylem delivers water for photosynthesis
phloem picks up sugars that have been produced in the palisade cells to transport to the rest of the plant (in the form of sap)

14. Lower surface (underside)
Also made of a layer of dermal tissue, but the cells are different
Guard cells allow gases to move in & out of the leaf
these cells have special pores called stomata
stomata are connected to the open spaces in the mesophyll
transpiration happens through these pores
CO2 enters, H2O and O2 leave
See Figure 2.8 on p. 61
transpiration = evaporation of water from the leaves

15. Chloroplasts: the Leaf’s Key Organelle
Located in palisade cells in the mesophyll
Where photosynthesis takes place
Palisade cells contain thylakoids
thylakoids = sacs that contain chlorophyll to trap light
when thylakoids are stacked, they are called granum (plural are grana)
See Figure 2.9 on p. 63

16. A 3D look at a leaf organ

17. The Stem Has 2 main jobs: Xylem & phloem tissues are found here
support
transportation of water, nutrients and sugars
Xylem & phloem tissues are found here
Both are made of vertically stacked tubes
Most of a plant’s xylem tissue is found in the stem
when xylem cells die, they provide long, fibrous ‘pipes’ that allow water to be transported easily
Phloem’s cell walls are porous to allow materials to move easily between phloem & neighbouring cells
Xylem & phloem are grouped together in vascular bundles
See Figure 2.10 on p. 64

19. The Roots Also has 2 main jobs:
anchor the plant to the ground
allow for water and minerals to be taken out of the soil
In some plants, the roots act like a storage area for starch & minerals
Special cells in the roots called cortex cells serve to store starch (long chains of glucose)
Endodermis tissue controls water and mineral flow to vascular tissues
Pericycle tissue surrounds the xylem and phloem
it allows roots to branch out
See Figure 2.11 on p. 65

20. Cross section of an Actual Root
Also see Figure 2.12 on p. 65

21. Types of Roots
1. Taproot
One main root that grows larger and thicker than the rest
Allows plant to reach far underground for water
ex: dandelion, thistle
2. Fibrous root
Thin, hair-like roots
Allows plant to absorb water from near the surface of the soil
Help prevent erosion
ex: grass, yarrow

22. Tissues in the 3 Main Organs